Method of electrolyzing alkali metal halide solution and apparatus therefor

ABSTRACT

A method for electrolyzing an alkali metal halide solution using a horizontal diaphragm electrolytic cell, wherein a diaphragm having a water-permeability of not more than 0.02 ml/cm2.cm H2O.hr is used, and water or an electrolytic solution is supplied to the underside of the diaphragm during electrolysis.

United States Patent [191 Motani et al.

[ METHOD OF ELECTROLYZING ALKAL! METAL HALIDE SOLUTION AND APPARATUS THEREFOR [75] Inventors: Kensuke Motani; Kinichi Yabuki;

Shunji Matsuura, all of Tokuyama; Sunao Tomoguchi, Shinnanyo; Yasuo Murata, Tokuyama, all of Japan [73] Assignee: Tokuyama Soda Kabushiki Kaisha,

Japan [22] Filed: Apr. 5, 1974 [21] Appl. No: 458,344

[301 Foreign Application Priority Data Apr. 10, 1973 Japan 48-39976 Sept. 17, 1973 Japan 48-103768 [52] U.S. Cl. .1 204/98; 204/128; 204/257;

204/258 [51] Int. Cl. COld 1/06; C0lb 7/06 51 Aug. 26, 1975 [58] Field of Search 204/128, 98, 258, 266, 204/257, 263, 255,256

[56] References Cited UNITED STATES PATENTS 1,222,239 4/1917 Ochs 204/266 1,598,018 8/1926 SChlumbergeL, 7777 4, 204/266 3,321,388 5/1967 Ueda et al. 204/98 3,770,611 11/1973 Barnabe 204/98 Primary Examiner-R. L. Andrews Attorney, Agent, or FirmSherman & Shalloway [57] ABSTRACT A method for electrolyzing an alkali metal halide solu tion using a horizontal diaphragm electrolytic cell, wherein a diaphragm having a water-permeability of not more than 0.02 ml/cm icm H Oihr is used, and water or an electrolytic solution is supplied to the un' derside of the diaphragm during electrolysis.

13 Claims, 8 Drawing Figures PATENTEU M182 6 I975 SHEET 1 BF 2 Fig. PRIOR ART PATENTED AUG 2 6 I975 SWEET 2 (IF 2 This invention r ls' r lfa. method for electrolyzing an aqueous solution of an alkali metal halide, and more Sp. sally t a moth "d for elcctrolyzing an alkali metal halide solution in a hrrirontni diaphragm cell using a diaphragm ha ing a low water-permeability, character wd in that water on an electrolytic solution is continu uslv cr intermittently supp ied to the underside of the diaphragm.

In the conventional electrolysis of alkali metal halidcs. the most preva...1'.. method is o use a vertical type electrolytic cell using on asbest s d aphragm. In this method. halogen gas generated on the anode surface and hydrocargar gene ated at the cathode surface rise through the s\ man on bo h 5 18's ct the diaphragm (muse-4n the cfi'scti area of passing electri=-ally d creases, and tlv: voltage between electrodes increases. Furthermore it is usually the practice in this method to pass 3;. aqueous solution of an alkali metal halide from an anode compa tment to a cathode compartment in order to prevent bases from diffusing rom the cathode compa tment to the anode compartment through the diaphragm. Therefore, the concentrations c bases gcneratrd in the cathode compartment. such odium hydroxide, potassium hydroxide, or o her 211 i hydronrles, decrease, and products containing alkali metal halides as impurities are formed. In order to remove these impurities. a complicated procedure is ul'rseourntly required, especially in a step of concentrating the caustic alkalies. Even when this procedure is taken, it is still impossible to reduce the content of the impurities to an extent comparable to that of a product obtained by the mercury method. Furthermore, an extracti g operation. for example, is required to remove the impurities.

with a iew to preventing the inclusion of impurities, attempts have ls-zcn made to use a cation permselective membrane (cation exchange membrane). The use of the cation exchange membrane results. in the prevention of diffusion 0:" boxes from a cathode compartment to an anode compartment, and in a high level of current efficiency maintained during electrolysis. Since the cation exchange membrane has a low water-permeability, the amounts of impurities that come into the product are reduced, and also alkali hydroxides of high concentrations can be obtained. In this case also, the defects inherent to the vertical structure of the electrolytic cell cannot be avoided, and the loss caused by a decrease in the effective arm. of passing electricity becomes greater with increasing current density.

Ordinary cation exchange membranes now under development cannot completely prevent the diffusion of bases, and therefore, the-re is a decrease in current effciency due to the ditfusion of bases.

In order to overcome such structural disadvantages, US. Pat. No. 3,770.61 1 proposes a horizontal diaphragm cell in which a diaphragm is disposed horizontally to divide the cell into an upper anode compartmerit and a lower cathode compartement.

In the horizontal electrolyte cell, a halogen gas evolved at the anode rises immediately without substantially passing the electrode urface. and it causes no substantial trouble. Hydrogen evolved at the cathode surface is taken out of the cell from the space under the cathode, and does not cause any substantial trouble.

Another advantage is that a space can be provided between the cathode and a reservoir for a catholyte (a solution containing caustic alkalies) within the cathode compartment, and therefore, caustic alkalies are prevented from diffusing into the anode compartment. However, when a diaphragm having a low waterpermeability or being substantially devoid of water-permeability is used in the horizontal electrolytic cell, and the cell is operated especially at a high current density, there is a great rise in temperature. Consequently, the humidity of the underside of the diaphragm and the cathode surface decrease and at times become dry, which in turn results in a rise in electric resistance and thus a rise in the electric voltage of the electrolytic cell, thereby causing a reduction in current efficiency. In an extreme case, the electrolysis fails.

An object of this invention is to produce alkali hydroxides having reduced amounts of alkali metal halide as impurities by electrolysis in accordance with the diaphragm method.

Another object of this invention is to provide an electrolyzing method using a horizontal electrolytic cell and a diaphragm having a low water-permeability.

Still another object of this invention is to provide a method in which an ion-exchange membrane is used as a diaphragm having a low water-permeability.

Still another object of this invention is to provide a method for electrolyzing alkali metal halide solutions while continuously or intermittently supplying water or an electrolytic solution to the underside of a diaphragm having a low water-permeability placed in a horizontal electrolytic cell.

Yet another object of this invention is to provide an apparatus suitable for performing the method of this invention.

Other objects of this invention along with its advantages will become apparent from the following descrip tion.

In the present invention, the same apparatus and operating procedure as the conventional horizontal electrolytic cells are used in many respects. The electrolytic apparatus used in this invention is one in which an anode compartment including an anode is disposed on the upper side and a cathode compartment including a cathode, on the lower side. Usually, a multiplicity of such units are superimposed, and used in the form of a multiple tier horizontal diaphragm cell.

The present invention provides a method for electrolyzing an alkali halide solution using a horizontal diaphragm electrolytic cell using a diaphragm having a water-permeability, as defined hereinbelow, of not more than 0.02 ml/cm .cmI-I,O.hr, characterized in that water or an electrolytic solution (these may be generically termed liquid" hereinafter) is supplied to the underside of the diaphragm. Where the electrolytic solution is supplied, it is desirable to use the same kind of electrolytic solution as the product, for example. a catholyte solution, in order to prevent the inclusion of impurities in the product. The liquid may be supplied from a separate source outside the electrolytic cell. Or the catholyte solution in the catholyte reservoir below the cathode compartment may be supplied either directly or after being taken out of the cell.

Since diaphragms of such a low water-permeability are used in this invention, the electrolysis is usually carried out in such a manner that alkali metal halides supplied to the anode compartment in the form of aqueous solution are consumed in an amount of not more than 60%, preferably to and the remainder of the alkali metal halides are withdrawn from the anode compartment as waste liquids and provided for reuse.

The invention will be specifically described by reference to the accompanying drawings in which:

FIG. I is a sectional view showing a known horizontal diaphragm-type electrolytic cell;

FIG. 2 is a sectional view showing the apparatus of this invention in which the liquid is supplied to the underside of the diaphragm by spraying it in atomized form from the bottom of the cell;

FIG. 3 is a sectional view showing another embodiment of the apparatus of this invention in which the liq uid is directly introduced to the underside of the diaphragm from outside the electrolytic cell;

FIG. 4 is a sectional view of the apparatus of this invention in which the liquid is discharged from the side wall of the cathode compartment;

FIG. 5 is a sectional view of the apparatus of this invention in which the catholyte solution is taken out from the catholyte reservoir by a siphon and supplied to the underside of the diaphragm;

FIG. 6 is a sectional view showing a similar structure to the apparatus shown in FIG. 3, wherein a levelling device is provided in order to supply the liquid smoothly;

FIG. 7 is a sectional view showing a liquid supply system for practicing the present invention with good efficiency; and

FIG. 8 is a sectional view showing an example of a liquid maintaining device.

There are only specific embodiments of this invention, and various changes and modifications are possible to those skilled in the art without departing from the spirit and scope of this invention.

In the drawings, the reference numeral I represents a diaphragm 2, a cathode 4, an anode 5, a feed inlet for an alkali salt solution 6, an outlet for halogen gas to be generated by electrolysis 7, an outlet for hydrogen gas 8, an outlet for alkali hydroxides 9, an anode compartment 10, a cathode compartment 1 1, a pipe for supply ing the liquid from outside the electrolytic cell I2, an inlet, preferably a spray nozzle, for supplying the liquid to the underside of the diaphragm and the cathode in the form of droplets uniformly 13, a capillary tube 14, a device for maintaining the water level constant IS, an outlet for withdrawing the alkali metal halide solution 3, a device for maintaining the liquid 16, a device for supplying the liquid to the underside of the diaphragm and the cathode by tapping the surface of the catholyte solution in the catholyte reservoir l7, a power transmitting device I8, a drive device I9, a device for actuating a switch in response to changes in electric voltage; and 20, a switch to be actuated by the switch actuating device l9.

As shown in FIG. I, in a well-known horizontal electrolytic cell, an aqueous solution of an alkali metal halide is introduced into an anode compartment partitioned by a diaphragm, for example asbestos paper, and it is electrolyzed while being passed to a cathode com partment. If desired a part of the anolyte is discharged from the anolyte outlet of an anode compartment. Halogen gas evolved in the anode compartment is discharged from the outlet. On the other hand, in the cathode compartment, hydrogen ions derived from water are reduced on the cathode generally disposed in full contact with the diaphragm or in close proximity to it, and hydrogen gas is generated. The alkali hydroxide solution is diluted with the aqueous salt solution that has passed through the diaphragm, and withdrawn from the outlet of the catholyte reservoir. The solution is generally an alkali hydroxide solution containing alkali hydroxides in a concentration of 0.5 to 4 normal and alkali metal halides of 50 to 200 mol% based on alkali hydroxides. Hydrogen gas is withdrawn from the outlet.

In actual operation, a multiplicity of cell units as shown in FIG. I are stacked, and one of such units will be described below. This, however, is not intended in any way to limit the number of cell units used in this invention.

The most basic embodiments of the present invention are shown in FIGS. 2 to 7, in which an electrolytic cell very similar to the well-known horizontal electrolytic cells is used. Thus, the conventional horizontal electro lytic cell can be easily modified for use in the practice of the present invention. In order to obtain high purity alkali hydroxides, there is used a diaphragm which permits the permeation of a very small amount of water or scarcely permits it. The permeating water consists of water permeated by the difference in pressure according to head under the electrolyzing conditions and water permeated by diffusion. The waterpermeability of the diaphragm used in this invention is not more than 0.02 ml., preferably not more than 0.0l ml., in terms of pressure difference owing to head of 1 cm of water per hour per cm". Most effectively, the amount of water to be permeated through such a diaphragm should be substantially negligible. In the present specification and the appended claim, the value expressed in a unit of ml/cm' cm H O. hr is defined as water-permeability. Accordingly, it is essential in the present invention to use a diaphragm having a water-permeability of not more than 0.02 rn|/cm .cm H O.hr., preferably not more than 0.01 ml/cm .cmH O.hr, more preferably substantially zero.

Generally, it is preferred to use cation exchange membranes. Such an ion exchange membrane is a membraneous substance resulting from the chemical bonding of a cation exchange group such as a sulfonic group, carboxyl group, phosphoric acid group, or phenolic hydroxyl group to a polymer having high chemical resistance and oxidation resistance. This ion exchange membrane usually has a water-permeability of not more than 0.02 ml/cm".cmH O.hr. For example, this membrane consists of a divinylbenzeneacrylic acid copolymer, a sulfonated high molecular substance such as a divinylbenzene-styrene copolymer, polyolefme, polyvinyl fluorocarbon ether or perfluoroethylenestyrene copolymer, or a composite of a cation exchange resin and another polymer. Nafion (tradename for the product of E. I. du Pont de Nemours & Co.) is a preferred diaphragm. Similar cation exchange membranes having fluorine atoms bonded thereto are also preferred. These membranes have desirable high degrees of electrolytic conductivity and high alkali ion transport numbers. The cation exchange membranes are disclosed, for example, in US. Pat. Nos. 2,636,85 I, 3,0I7,338, 3,496,077, 3,560,568, 2,976,807, and 3,282,975, and British Pat. No. l,l84,32l.

It is also essential that water or an electrolytic solution should be supplied continuously or intermittently to the underside of the diaphragm, or both to the underside of the diaphragm and the cathode.

Examples of the method of supplying water or the electrolytic solution are shown in FIGS. 2 to 7, but other means can also be applied.

As shown in FIGS. 2 to 4 and 6, water or the electrolytic solution may be supplied from outside the electrolytic cell. Alternatively, the catholyte solution may be directly fed as illustrated in FIGS. 5 and 7. The modes of supplying water or the electrolytic solution include, for example, one wherein it is supplied in the form of droplets by a spray nozzle (FIG. 2); one wherein the liquid is supplied under pressure from ajet outlet (FIG. 4); one wherein the liquid is sprayed uniformly by a sprinkler statistically, or supplied by gravity (FIGS. 3 and 6); one wherein it is supplied by a capillary action (FIG. 5 and one wherein the liquid is scattered by tapping the liquid in the catholyte reservoir using a rotating blade. for example (FIG. 7). These modes of liquid supply may be used individually or in combinations in the present invention.

The liquid to be supplied is water or an electrolytic solution. In particular, by supplying water or an alkali hydroxide solution in a suitable concentration, the alkali hydroxide to be withdrawn from the electrolytic cell as a product can be adjusted to the desired concen tration. The minimum amount required of the liquid to be supplied to the underside of the diaphragm is that required to maintain good conductivity for passing electricity between the anode and the cathode. Since a diaphragm having a low water-permeability is used in this invention. sufficient electric conductivity for the electrolytic solution cannot be maintained only by the water which passes through the diaphragm in the form hydrated to the alkali metal ion passing thercthrough (usually, 2 to 8 molecules of water per alkali metal ion) and the water present in the alkali metal halide solution passing through the diaphragm by the water-permeability of the diaphragm. Accordingly, the water should be supplemented with a fresh supply of water or aqueous solution in order to secure the minimum required amount of water. In general, the temperature becomes higher when the electrolysis is carried out at a high current density, and the evaporation of water from the vicinity of the underside of the diaphragm becomes vigorous, with the consequence that the minimum amount required of the liquid tends to be larger. The minimum required amount of the liquid to be supplied is determined by the minimum amount required to prevent a rise in voltage during electrolysis. In determining this, there is employed a method wherein a standard voltage is set within a predetermined range of the voltage of the electrolytic cell, for example, 2 to 5 volts, and a voltage value higher than the predetermined value, for example, by 10%, preferably by 5%, is set as an upper limit voltage, and when the electrolyiing voltage exceeds the upper limit, the liquid is supplied until the voltage re turns to the standard voltage, or the liquid is supplied continuously or intermittently so that the electrolyzing voltage is maintained within the range of the standard voltage predetermined.

The provision of the liquid maintaining device in contact with the underside of the diaphragm and the surface of the cathode is also a preferred embodiment in this invention. Several examples of this embodiment are shown in FIGS. 3 to 6, and an example of providing the liquid maintaining device is shown in FIG. 8.

FIG. 8 is an enlarged view showing the provision of the liquid maintaining device between the diaphragm and the cathode. The liquid maintaining device is one which has the ability to maintain the wet state and has a relatively high durability to alkali hydroxides, and its material and shape are not restricted in particular. Examples of the material of the liquid maintaining device are inorganic fibrous materials such as asbestos or glass fibers, or woven fabrics, non-woven fabrics, mats or battings thereof; porous open-cellular substances composed of a resin having a relatively high resistance to alkali such as vinylidene chloride resins, polyolefin resins, fluorine-containing resins, polyester resins or polyamide resins, woven fabrics or non-woven fabrics composed of fibers made from such resins; porous ceramics or minerals such as biscuits or porous stones; and porous metalsv Generally, materials having the ability to maintain the liquid by a capillary action or the hydrophilicity of their surfaces.

The cathode can be constructed in a porous structure having a porosity of, say, at least preferably at least From the viewpoint of the current efficiency and the mechanical strength, it is preferred that the porosity of the cathode should be not more than about By using a porous metal or wire gauze having pores permitting passage of solution and having an average unit pore area of not more than I cm preferably not more than 3 mm as the cathode, it can concurrently maintain the liquid by itself without using a liquid maintaining device. Needless to say, such a cathode can be used together with another liquid maintaining device.

In one preferred embodiment of the present invention as shown in FIG. 7, the liquid is supplied to the underside of the diaphragm by actuating the liquid supply means 16, such as rotary blades, through drive means 18 and power transmitting means 17 to be operated by the closing or opening of the switch 20 to be actuated in response to signals from the device I9 which automatically measures the voltage between the anode and the cathode and emits signals when the voltage exceeds the predetermined upper voltage or returns to values within the predetermined range. When sufficient elec tric conductivity within the diaphragm and between the diaphragm and the cathode is restored, and the voltage becomes normal below the upper limit, the switch is automatically opened to stop the supply of the liquid. By using such a device, the electrolysis of alkali metal halide solutions can be performed in stable condition with good current efficiency.

The alkali metal halide solutions to be electrolyzed by the method of this invention are salts formed between alkali metals selected from lithium, sodium, potassium, rubidium and cesium and halogens selected from chlorine, bromine and iodine. Typical examples of such salts are sodium chloride, potassium chloride, sodium bromide and potassium bromide. With certain alkali metal halides, the halogen cannot be recovered as a gas by electrolysis, but this does not affect the principle of this invention.

Thus, according to this invention, alkali hydroxides can be obtained as solutions of high concentrations such as 2N to ISN, and the concentration of salts present as impurities can be reduced to not more than 10 mol% based on caustic alkali, for example to less than F71.

The following Examples illustrate the present invention without any intention to limit the present inventlon.

EXAMPLE 1 A saturated saline water was electrolyzed using a horizontal electrolytic cell made of an acrylic acid resin shown as FIG. 2 (effective area of diaphragm 100 mm X 100 mm). The cell was modified to secure a water supply pipe to the cathode compartment, and an Rh-Ti anode and a cathode in the form of an Ni porous plate having a porosity of 71% were used. A 3N aqueous solution of sodium hydroxide was continuously fed in the atomized form to the underside of the diaphragm and cathode at a rate of 25 ml/min.. A part of the caustic withdrawn from the cathode compartment was used for analysis. A predetermined amount of water was continuously supplied to the catholyte reservoir so as to maintain the concentration of the caustic soda withdrawn from the tank at 3 N. The diaphragm used was a cation exchange membrane of a fluorine resin type having a water-permeability of substantially zero. The electrolyzing conditions and the results obtained are shown in Table 1 below.

The above procedure was repeated except that instead of the 3N caustic soda, water was fed to the underside of the diaphragm and cathode in the atomized form, and instead of the water to be supplied to the reservoir of the catholyte solution in the above procedure, water was intermittently sprayed at a rate of 200 ml./hour.

In either case, similar results were obtained.

The results shown in Table l were average of values after operating for 2 months.

lytic cell EXAMPLE 2 The procedure of Example l was repeated except that an Ni wire gauze having a porosity of 64% was used as the cathode. The current efficiency was 92%, and the voltage of the electrolytic cell was 4.] V.

Comparative Example 1 The procedure of Example 2 was repeated except that water was neither supplied to the cathode compartment nor sprayed. A catholyte solution having an NaOH concentration of above 40% could be obtained, but the voltage of the cell was as high as above 7, and the current efficiency was as low as 60%. The operation for a short period of time could be performed, but because NaOH of high concentration passed through the cathode and the diaphragm surface, and the amount of the liquid was small, an electric current had difficulty of flowing, and the voltage rose, and further the current efficiency was poor. Accordingly, this operation is not economical, and is not suitable for use in commercial operation.

EXAMPLE 3 Electrolysis was performed using a horizontal electrolytic cell made of chlorinated polyvinyl chloride resin (effective area of diaphragm 500 mm X 500 mm), a porous plate cathode having a porosity of 71%, and an Rh-Ti anode. An alkali solution was performed in the same way as in Example 1 using a sulfonic acid-type cation exchange membrane made of styrenedivinylbenzene copolymer with polypropylene as a backing material and having a water-permeability of substantially zero. The electrolzing conditions and the results obtained are shown in Table 2.

electrolytic cell When pure water was not fed into the cathode compartment in this Example, the concentration of sodium hydroxide formed was 590 g/l, and the operation could be performed continuously.

EXAMPLE 4 A horizontal electrolytic cell made of an acrylic acid resin (the effective area of diaphragm mm X [00 mm) was used which included an Rh-Ti anode and a cathode of an Ni porous plate. A cation exchange membrane of the sulfonic acid type with styrene/divinyl benzene copolymer having a water-permeability of less than 0.02 was brought into contact with the cathode with a water maintaining material made of a polypropylene non-woven fabric disposed therebetween. The liquid was fed to the diaphragm using four siphons made of polyvinyl chloride tubes and each having a diameter of 4 mm. The electrolyzing conditions and the results obtained are shown in Table 3.

clectroxidc solution formed lysis Table 3-Continued Table S-Continued Current efficiency based on 93% Electrolyzing temperature Gtfi. sodium hydroxide Current density 30 A/dm Voltage of the electrolytic 4.4 V cell 5 Concentration of sodium hydroxide 130 g/l formed Results Concentration of sodium chloride of in the resulting sodium hydroxide 0.2 g/l I electrosolution Comparative Example 2 lysis Current efi'iciency based on sodium 91% hydroxide Electrolysis was performed under the same condi- Voltage of the electrolytic cell 45 -4.7 tions as in Example 4 using a vertical electrolytic cell (the effective area of the diaphragm 200 mm X 50 mm). The current efficiency was 88%, and the voltage EXAMPLE 8 of the electrolytic cell was 4.9 V. g

Electrolysis was performed under the conditions EXAMPLE 5 shown in Table 6 in the same way as in Example 1 ex- The procedure of Example 4 was repeated except cepcti that adsatfurlzlited tpotassciumrchloride solution was that instead of the polypropylene non-woven fabric, use mstea 0 t e 83 rate same water there was used a porous film obtained by molding a Table 6 mixture ofa polypropylene resin, a surface active agent and magnesium carbonate, and extracting the molded Concentration of the salt solution 320 g/l fed article with 2N hydrochloric acid. The current effi Elccmh PH 0f the Sun solution fed 4 ciency was 94%, and the voltage of the electrolytic Cell lyzing was 4 1 v con- Concentration of the salt 260 g/l ditions solution discharged Electrolyzing temperature 60C. EXAMPLE 6 Amount of pure water fed 200 ml/hour 2 Electrolysis was performed using a horizontal elec- Cunent dens'ty 20 Alum trolytic cell (the effective area of diaphragm 500 mm Concentration of potassium hydroxide I54 g/l X 500 mm) made of a thermally stable vinyl chloride formed resin including an Rh-Ti anode and a cathode made of Results Concentration of potassium a 6-mesh wire gauze. The diaphragm consisted ofa sulthc l' pmass'um electrohydroxide solution fonic acid type cation exchange membrane made of a lysis styrene/divinylbcnzene with polypropylene as a backemcenclf based 94 potassium hydroxide mg material. The method of supplying water was the same as in Example 4. The electrolyzing conditions and Vflllage of the electmlytic V the results obtained are shown in Table 4.

Table 4 What we claim is:

l. A method for electrolyzing an alkali metal halide Concentration ofthe salt snlu- 31 g/l 40 solution using a horizontal diaphragm electrolytic cell, fed wherein a diaphragm having a water-permeability of con- Concentration of the salt solution 260 g/l not more than 0.02 ml/cm .cm H 0.hr is used, and discharge? water or an electrolytic solution is supplied to the un- Electrolyzing temperature 80%v .I Amount of pure fed 5 who, derside of the diaphragm during electrolysis. Current density 30 A/dm 2. The method of claim 1 wherein said diaphragm is a cation exchange membrane. Concentration of sodium h droxide Hi0 g/l ("mad y 3. The method of claim 1 wherein the supply of water Results Gmcemmlio" of 9 chkljide or an electrolytic solution is performed continuously. of in the resulting sodium hydroxide 0.3 g/l electm min" 4. The method of claim 1 wherein said water or eleclysis 50 trolytic solution is supplied when the voltage of the m i based 88% electrolytic cell exceeds a predetermined standard voltsodium hydroxide Voltage of the electrolytic cell 4.4 V ag 5. The method of claim 1 wherein said electrolytic solution is a catholyte solution.

6. The method of claim 1 wherein the su l of water EXAMPLE 7 pp y Electrolysis was carried out under the conditions shown in Table 5 using a horizontal electrolytic cell (the effective area of diaphragm 100 mm X 100 mm) made of an acrylic acid resin and having the structure shown in FIG. 7. The results are shown in Table 5.

or an electrolytic solution is performed intermittently.

7. A method for electrolyzing an alkali metal halide solution using a horizontal electrolytic cell, wherein a cation exchange membrane having a water-permeability of not more than 0.02 ml/cm .cm H O.hr is used as a diaphragm, a wire gauze or porous plate having a porosity of at least 50 is used as a cathode, and water or an alkali hydroxide solution is supplied to the undersidcs of the cathode in the form of atomized spray or jet during electrolysis,

10. The electrolytic cell of claim 9 wherein means for supplying the liquid is a sprayer.

ll. The electrolytic cell of claim 9 wherein means for supplying the liquid is a siphon,

12. The electrolytic cell of claim 9 wherein means for supplying the liquid is a rotating blade.

13. The electrolytic cell of claim 9 wherein means for supplying the liquid is a sprinkler said said

said

said 

1. A METHOD FOR ELECTROLYZING AN ALKALI METAL HALIDE SOLUTION USING A HORIZONTAL DIAPHRAGM ELECTROLYTIC CELL, WHEREIN A DIAPHRAGM HAVING A WATER-PERMEABILITY OF NOT MORE THAN 0.02 MI/CM2.CM H2O.HR IS USED, AND WATER OR AN ELECTROLYTIC SOLUTION IS SUPPLIED TO THE UNDERSIDE OF THE DIAPHRAGM DURING ELECTROLYSIS.
 2. The method of claim 1 wherein said diaphragm is a cation exchange membrane.
 3. The method of claim 1 wherein the supply of water or an electrolytic solution is performed continuously.
 4. The method of claim 1 wherein said water or electrolytic solution is supplied when the voltage of the electrolytic cell exceeds a predetermined standard voltage.
 5. The method of claim 1 wherein said electrolytic solution is a catholyte solution.
 6. The method of claim 1 wherein the supply of water or an electrolytic solution is performed intermittently.
 7. A method for electrolyzing an alkali metal halide solution using a horizontal electrolytic cell, wherein a cation exchange membrane having a water-permeability of not more than 0.02 ml/cm2.cm H2O.hr is used as a diaphragm, a wire gauze or porous plate having a porosity of at least 50 % is used as a cathode, and water or an alkali hydroxide solution is supplied to the undersides of the cathode in the form of atomized spray or jet during electrolysis,
 8. A method for electrolyzing an alkali metal halide solution using a horizontal electrolytic cell, wherein a cation exchange membrane having a water-permeability of not more than 0.02 ml/cm2.cm H2O.hr is used as a diaphragm, a liquid maintaining material is disposed in contact with the underside of the cation exchange membrane and the cathode surface, and water or an electrolytic solution is supplied to the liquid maintaining material during electrolysis.
 9. A horizontal diaphragm electrolytic cell including a diaphragm having a water-permeability of not more than 0.02 ml/cm2.cm.H2O.Hr and means for supplying a liquid to the underside of the diaphragm.
 10. The electrolytic cell of claim 9 wherein said means for supplying the liquid is a sprayer.
 11. The electrolytic cell of claim 9 wherein said means for supplying the liquid is a siphon.
 12. The electrolytic cell of claim 9 wherein said means for supplying the liquid is a rotating blade.
 13. The electrolytic cell of claim 9 wherein said means for supplying the liquid is a sprinkler. 